The present invention relates generally to apparatus and methods for the treatment of vascular disease and particularly to apparatus and method for treatment of cerebral aneurysms, arterial vascular malformations and arterial fistulas using lasers.
Cerebrovascular disease is the third leading cause of death in the United States, ranking behind only coronary artery disease and cancer. This disease can take several forms, including but not limited to cerebral aneurysm, arterial venous malformations (AVMs) and arterial fistulas (collectively referred to hereafter as xe2x80x9caneurysms.xe2x80x9d) One of the most important forms of this disease is the cerebral aneurysm, which manifest itself as a dilatation, or pouching of the arterial wall. As the disease progresses, the dilatation develops into a distended sac of thinned, stressed arterial tissue with a size of 5 to 10 mm in diameter. If not treated, an aneurysm continues to grow until it ruptures, causing a subarachnoid hemorrhage (that is, bleeding between the middle membrane covering of the brain and the brain itself), severe neurological complications, and, possibly, death.
The components of the arterial wall that are primarily responsible for its mechanical strength and elasticity are the structural proteins collagen and elastin. Collagen, which serves a protective function, is very extensible and breaks at a stress of about 500 megapascals. Collagen is the substance that gives the artery wall its high resistance to the hemodynamic forces created by the heart pumping the blood through the vessel. Elastin fibers, on the other hand, can stretch to about 250% of their original length and have about 20 times lower modulus of elasticity than collagen. These two proteins cooperate to provide vessels with sufficient strength and flexibility to withstand the continuous pounding and pressure of the blood as it flows through the vessel in response to the beat of the heart.
A fully developed cerebral aneurysm, however, consists almost entirely of collagen fibers, because the majority of the elastin fibers are fragmented by the distending forces of blood pulsating through the vessel in response to the rhythmic beat of the heart. This loss of elastin fibers is especially true for the top of aneurysm, where the tissue degradation is more advanced than in the base and the sidewalls of the aneurysm. Most ruptures consequently occur at the top, or dome, of the aneurysm. The aneurysm ruptures when its wall become too thin to withstand circumferential stresses imposed by the pressure differential between the arterial lumen and the subarachnoid space outside the artery.
Each year about 30,000 North Americans are diagnosed with a ruptured aneurysm and more than half of them die within the first thirty (30) days thereafter. Diagnosis and successful treatment of an aneurysm prior to its rupture is therefore critical to improving the survivability of a patient to this disease. The fundamental objective in the management of an aneurysm that has not ruptured is to stabilize it, thus avoiding further dilatation or growth. Aneurysm stabilization is currently accomplished by:
1) Conventional neurosurgical intervention, which cuts off the blood flow from the vessel to the aneurysm by ligating its neck with a metal clip;
2) Endovascular embolization with metallic or other solid mechanical objects causing thrombosisxe2x80x94clottingxe2x80x94inside the aneurysm; and
3) Thrombus generation within the aneurysm by heating the blood with a catheter having an insulated heating coil at its distal end.
An example of the endovascular approach is given in U.S. Pat. No. 5,354,295 entitled xe2x80x9cAn Endovascular Electrolytically Detachable Wire And Tip For The Formation Of Thrombus In Arteries, Veins, Aneurysms, Vascular Malformations And Arteriovenous Fistulasxe2x80x9d issued on Oct. 11, 1994 to Guido Guglielmi at al. In this patent a method of treatment of aneurysms is described, in which an aneurysm is packed with detachable platinum wires, causing blood stagnation and blood clot formation inside the aneurysm. The clot prevents arterial blood from reaching the cavity of the aneurysm and continuing to apply pressure to the wall of the aneurysm and helps to stabilize the aneurysm.
In U.S. Pat. No. 5,919,187, issued on Jul. 6, 1999 to Guido Guglielmi, and entitled xe2x80x9cMethod And Apparatus For Endovascular Thermal Thrombosis And Thermal Cancer Treatment,xe2x80x9d a method and apparatus for endovascular thermal thrombosis is described. In this version of the endovascular approach to treatment, a thrombus is generated in an aneurysm, arteriovenous malformation (AVM) or fistula by heating the blood with a catheter having an insulated heating coil at its distal end.
The described methods are not applicable to aneurysms that do not have obviously defined necks (narrow openings between the artery and the aneurysm sac). Such aneurysms can""t hold the wires or other emboli inside the cavity. Another shortcoming of the described methods is that the blood clot, formed by blood stagnation inside the cavity or its heating, is relatively weak. The fresh arterial blood, coming into the aneurysm can cause lysis (dissolution) of the clot inside the sac and create a chance that a piece of wire or a piece of clot can be displaced from the aneurysm into the blood stream and embolize distally.
A new treatment is needed that is free from these shortcomings and will improve the stabilization of aneurysms by improved methods and apparatus. The present invention provides an apparatus and method that stabilizes aneurysms of different shapes and produces a clot that is much more resistant to wash out by the blood flow.
The invention is an apparatus and method for forming a mural arterial thrombus, that is, a thrombus grown on and attached to the vascular wall inside a cerebral aneurysm, with emphasis on the formation of the arterial thrombus on the inner surface of the dome and the neck of the aneurysm.
In the present invention, formation of the desired arterial thrombus begins with an injury to the endothelium of the vascular wall of the aneurysm. This injury, which triggers the coagulation sequence within an aneurysm, is created by ultraviolet (UV) radiation delivered to the inner surface of the aneurysm by a micro catheter. The micro catheter comprises a steerable guide wire with an optical fiber in it. The proximal end of the optical fiber is coupled to a laser capable of producing (UV) radiation. The distal end of the guide wire, which emits UV radiation scattered in different directions, is placed inside the aneurysm. A dose of UV radiation, sufficient to cause complete necrosis of the endothelium and lead to the formation of the arterial thrombus, is delivered to the whole surface of the aneurysm.
Preferably, the blood is displaced from the aneurysm by a UV radiation transparent fluid, such as saline. Saline for this purpose may be delivered into the aneurysm from a pressurized saline bag or by a pump outside the patient via a plastic micro tube placed over the guide wire. In one implementation of the present invention a soft balloon, secured around the plastic micro tube, temporarily occludes the artery, thus ensuring better transparency inside the aneurysm. After delivery of the appropriate dose of UV radiation, the saline wash is terminated allowing blood to flow again into the aneurysm.
In another implementation of the invention an optical fiber (or multiple fibers) is placed inside the wall of the plastic micro tube delivering saline to the aneurysm. In this case a conventional guide wire is used for placing the tip of the micro catheter inside the aneurysm, and the blood flow in the feeding artery is not occluded even temporarily. The UV radiation is delivered to the aneurysm wall in the same manner as in the first implementation.
The foregoing method also may be used for the treatment of AVMs and arterial fistulas.
The foregoing objects of the invention will become apparent to those skilled in the art when the following detailed description of the invention is read in conjunction with the accompanying drawings and claims. Throughout the drawings, like numerals refer to similar or identical parts